The present invention relates generally to an apparatus for observing or examining surface geometries and physical properties of a specimen. More particularly, the invention is concerned with a method and an apparatus for obtaining information concerning surface geometries, physical properties, magnetic and electric or like properties of a specimen and/or information concerning thickness, properties or nature of insulation film or the like deposited on a specimen surface by making use of an atomic force, a magnetic force, a tunneling current or the like which becomes effective or takes place between a probe and a specimen surface when the probe is moved closely toward the specimen surface in a relative sense, such as by an atomic microscope, a magnetic force microscope or a like surface observing or examining apparatus.
In the state of the art which the present invention concerns, there is proposed and discussed an atomic force microscope for observing or examining a surface of a specimen by scanning it with a probe mounted on a cantilever at a free tip end thereof while maintaining a constant a force of an extremely or infinitesimally small magnitude (repulsive force or attraction) acting between the probe and the specimen surface by detecting displacement (or deflection) of the cantilever by means of an STM probe and maintaining constant displacement of the cantilever through a servo control. In this conjunction, reference may be made, for example, to U.S. Pat. No. 4,724,318 (which corresponds to JP-A-62-130302). Further, a method of detecting a force gradient acting on a probe while vibrating the latter is described in "Journal of Applied Physics", Vol. 61, pp. 4723-4729 (1987).
With the techniques known heretofore such as those mentioned above, a surface structure of a specimen can be observed by controlling a position of a probe such that a force acting on the probe is held to be constant. Furthermore, a magnetic stray field and/or an electric stray field prevailing above a specimen surface can be measured or determined on the basis of the force gradient as detected. However, it is impossible to know at what height or distance the magnetic stray field and/or electric stray field is present above the specimen surface or what correlation exists between a surface structure of the specimen and the magnetic stray field or the electric stray field. Further, in addition to the measurement of an extremely small force acting in the direction perpendicular to the specimen surface, it is equally desirable to be able to measure an infinitesimal force in the horizontal direction (i.e., intra-plane direction), from the viewpoint of determination of a frictional force and a magnetic force. However, measurement of the force in the horizontal direction was heretofore impossible.